The great energy content in the fluidized bed ina PFBC power plant entails particular problems at a load drop and tripping of the gas turbine. The supply of energy from the combustion chamber must be rapidly cut to prevent the speed of the turbine from increasing to a dangerous level. Shut-down valves are provided in the hot-gas pipe between bed vessel and turbine and in the air duct between compressor and bed vessel or a pressure vessel surrounding the bed vessel. The plant also includes a by-pass conduit or short-circuit pipe between the hot-gas pipe and the air duct. This by-pass pipe contains a valve which, when the gas turbine trips, opens to provide direct communication between compressor and turbine. U.S. patent application Ser. No. 007,226, filed Jan. 27, 1987 describes a PFBC power plant of this type, and how such a plant can be controlled in the event of the gas turbine tripping at a load drop.